EBOOK
A PART NUMBER
ANTHOLOGY
Table of Contents
Part Revisions: Deal or No Deal
4
Supplier Part Numbers: Hidden Surprises
12
What’s the Great Part Number Debate? 17
The One True Part Number System
25
Introduction
Part numbering. For most engineers, this two-word phrase is all it
takes to conjure up especially strong feelings about what it means
to be “right”, and what it means to be very, very “wrong.”
Intelligent numbering? Generic numbering? Pick a side that’s
burned you the least and stick to it. It’s a cold world out there for
fence sitters. Ask us how we know (or just read the final chapter).
As is true with all questions metaphysical, it helps to write your
thoughts down. So we did. And then we invited a free and open
dialogue. Sometimes you disagreed with us, sometimes you
didn’t, and sometimes you simply commiserated.
When it was all said and done, we assembled this anthology. At
the end of each chapter you’ll find our favorite snippets from the
discussion, from author and reader alike. And if you’re not satisfied with where we left it, you know how to get a hold of us.
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Part Revisions: Deal or
No Deal
Ed Lopategui
P
arts don’t have revisions. Such a broad statement seems a
little absurd especially considering today’s available software
technology, but it’s nonetheless a long-held tenet of engineering
configuration management.
While it might appear outlandish to set such a seemingly arbitrary
restriction on engineering process, there are sound reasons why
the advice holds true. But before you make a unilateral decision
never to revise a part, let’s understand just why such thinking became an accepted standard. Then you can make judicious and
informed decisions with your own engineering design.
What do we mean when we say parts don’t have
revisions?
A part is identified by a Part Identification Number (PIN), aka the
part number. If you were holding the part in your hand, this is
what would be physically emblazoned upon it. A part is also accompanied by documentation that plainly and precisely describes
the part model. In many cases, the documentation is a fully diGRABCAD.COM
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mensioned engineering drawing, though these days it might also
be Product Manufacturing Information (PMI), if you’re riding the
technology wave. In the case of a drawing, the documentation
also carries an identifying number. While it may be tempting to
make the part and drawing numbers the same, such an approach
aims to misbehave. For example, a drawing is often changed for
very different reasons than the part it describes, often in a fashion that has no impact on design. In addition, drawings may describe multiple parts. In other words, drawing and part life cycles
are unique, so the identification number for each must also be
unique.
Documentation can be revised, but the part itself should not. If a
part changes, the revised part is issued a new part number. In the
case of PMI, where the "documentation" portion is integral to the
part, revisions are more esoteric. Allowable PMI revisions in that
case depend on whether the documentation portion is being updated or the part model is being physically changed.
Why can't parts be revised?
It’s all about how parts are consumed in manufacturing. Parts are
ordered, processed, and stocked by part number, not revision.
Issuing a new part number for changes addresses the following:
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• Existing Stock: The prior part didn't just spontaneously cease
to exist; it's still in inventory and it may continue to live on in
products that may already be sold, delivered, or in use. It's
important to distinguish between these to control how the
change might or might not be propagated.
• Alternate Uses: If a part is used in multiple applications, then
a favorable change for one application may be detrimental to
the second. It's critical to keep such histories separate and distinct.
• Failure Modes: If two parts carry the same identification, but
are functionally different, or are used for different purposes,
confusion is inevitable. Confusion can lead to failure and liability.
Exception for Interchangeability
It might seem costly to constantly issue new part numbers for
every tweak and adjustment. Especially if a change in a component part causes the next higher assembly to behave differently
and propagate additional part number changes. This is where
interchangeability comes into play, more commonly known as the
"Three F’s:"
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• Form: The physical nature of the part, including its strengths
and weakness, structural or otherwise.
• Fit: How the part interacts with other parts.
• Function: What the part actually does.
The interchangeability rule states if a part modification does not
appreciably affect the form, fit, and function of the part, then the
modification is deemed interchangeable. Here, a new part number is not required. In other words, if you were to blindly reach
in a bucket with both versions of the part, it wouldn't matter at
all which you would pull out. As you can imagine, few changes are truly considered interchangeable.
When traversing a
change up an assembly structure, engineering judgment is used
to determine the point of interchangeability (i.e. where part
numbers stop changing).
Other Options
Someone might guess that if a part is identified with the part
number and the revision level, then the problem is solved. But
that's not the case. Instead, revision level has become nothing
more than an extension of the part number, so the manufacturGRABCAD.COM
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ing impact is the same as if everything was not interchangeable!
Additionally, most manufacturing processes don't accept such a
concept because parts are not ordered, processed, and stocked
by revision level.
One permissible use of revisions is pre-production. Many changes
occur while a part is in the concept stage. Without a supply chain
consideration, it’s okay to revise parts, as long as you don’t intend
to use the prior part revisions in production.
Remember
Deal—When to revise a part:
Interchangeable modifications
Pre-production parts
No Deal—When to issue a new part number:
Non-interchangeable modifications
New applications for an existing part
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DISCUSSION
Dean:
This is a paper-based (old school) method of operation. The industry is headed toward MBD (model-based definition, or MBE, model-based enterprise), in which a single file defines the cad model,
GD&T, drawing, material/coating info, FEA model, CFD model, marketing plan, assembly procedure, costing details, eBOM, CAM file,
assembly video, and anything else you can think of in a single opensource format (HTML or pdf) that can be opened on a cell phone
or any other device. This MBD is eluded to in MIL-STD-31000A and
ASME Y14.41. All that to say that this article describes a paper-based
system that has been around since the 50’s, which is being phased
out. Many companies have already moved towards “rev-locking” their
designs, which is a partial solution to MBD. Once industry software
solutions are mature enough, it will be easy to complete the jump
and have a single file design--hence, no need to track multiple files
describing a single part or assembly...and no dash numbers.
Ed Lopategui:
Dean, thanks for the thoughtful comment.While I agree that MBD is
the future, I’d caution to say that the future is very much a work in
progress. People are likely to get a little upset about either half of
that sentence, depending on their perspective.
More importantly, the problems I describe aren’t an artifact of documentation, they are fundamental configuration management issues.
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Two parts carrying the same identification but with different form, fit,
and function is a problem. That’s true whether the part is defined on
dusty prints sitting in a file cabinet, or an open source container on
your shiny new smart implant. It’s not about the number of files, it’s
about interchangeability and the consequences that follow.
The universal all-encompassing (and even open source!) format that
you mention is often promised and certainly desired, but no one has
yet delivered. We still have a long way to go. One day...
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Supplier Part Numbers:
Hidden Surprises
Ed Lopategui
S
omewhere lurking in your Bill of Material (BOM), there just
might be a hidden surprise, and not the good kind of surprise
with cake and balloons.
We're talking about the type of surprise that you probably hate;
one that costs you time and money (not to mention a little aggravation). The puzzling truth is that surprise can hide in plain sight,
in something you might think as rather ordinary: the supplier part
number. But what impact could something as simple as a part
number really have, after all?
You'll find most good configuration management practice is careful to differentiate between Internal Part Numbers (IPN) and Manufacturer Part Numbers (MPN) aka supplier part numbers. Internal part numbers are uniquely defined and controlled by your
company. Supplier part numbers are not. Whether or not you
have control over a part number is rather important, which is why
the prevailing recommendation is to keep supplier part numbers
out of your BOM. There are some exceptions of course, including
parts defined by a recognized industry or international standard
such as the National Aerospace Standards (NAS) or the former
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military standards. Supplier part numbers can be added as metadata, included in auxiliary reference columns, or digitally associated to the supplier numbers within your BOM Management or
Enterprise Resource Planning (ERP) tool. But why? The underlying
strategy is to isolate the engineering design from supply chain requirements. You don't want to be constantly updating the former
to keep up with the latter.
With that in mind, below are some of the hidden surprises you
might discover:
• Supplier Part Number Changes: Each supplier, like your own
company, maintains their own internally developed part numbering system. At any time, that system can change in whole
or in part, for reasons that will not at all be transparent to you.
Due to mergers and acquisitions or internal process change,
it's not all that uncommon for supplier part numbers to
change or be re-characterized entirely. If you're carrying such
supplier part numbers directly in your BOM, you'll have a really
bad day chasing down changes that have nothing to do with
your design.
• Fighting Internal Process: It's important to maintain consistency in your company numbering methodology. While we'll
leave the quasi-religious debate over using intelligent or generGRABCAD.COM
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ic numbering systems for some future blog post or three, the
point is you probably have tools to help support your company's
numbering system. Accommodating a wide variety of foreign
part numbers is not worth the hassle, it's better to abstract that
information as part of your supply chain management.
• Supplier / Source Changes: Depending on your specific requirements, many parts can be sourced by multiple suppliers..
Alternates and substitutes may be available and their relative
supply will ebb and flow over time. Trying to keep up with this
in a BOM is not a constructive use of your time. The sourcing
and substitution information can be associated to your internal number. Additionally, as your requirements change you
can leverage your internal number into a full source control or
even a selected item designation for more tightly controlling eligible parts from a design context, if the application demands.
• Numbering Collisions: In all of their seemingly infinite variety,
supplier part numbers might seem like snowflakes. But part
numbers in fact are not snowflakes. As many companies have
adopted generic numbering methodologies, the chances of collisions in some circles have actually increased. The last thing you
need to deal with is pulling apart the overlap of two completely
different parts, one of which has nothing to do with your design.
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So next time you think about straight up popping a supplier part
number into your BOM and think nothing of it, keep the above in
mind. You just might be in for a surprise.
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What’s the Great Part
Number Debate?
Ed Lopategui
W
hat's in a part number? That which we call a part by any
other number should assemble as easily? Every company
struggles with defining part numbers. Should you use an intel-
ligent numbering system that embeds important identifying information or go with easy-to-mange generic numbers? Choosing
between these opposing methodologies might seem intimidating;
solid arguments exist for either approach. Crowning a winner is
not going to be constructive, but understanding how the underlying issues affect your company certainly will be.
Creation and Data Entry
Generating a new number should be easy, even for the new intern. Nothing is easier than a system-assigned generic number.
PDM/PLM systems default to a generic numbering system, but
that is neither a recommendation nor a limitation. Most modern
systems can accommodate intelligent numbering without heavy
customization and/or manual entry. If you choose to embed intelligent information, you are trading the simplicity of creating
a part number for a downstream benefit, so weigh that benefit
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carefully. Consider the part number is often what you start with
on new design.
How much will you know at that stage and how certain are you
about it? Could that information change in the future? Such considerations will help determine what information, if any, is truly
practical to embed in an intelligent number.
Longevity and Legacies
You want your part numbers to last. Intelligent numbering systems tend to break down over time, especially if the intelligence is
used for complex categorization. It probably won't be tomorrow,
or next week, but a couple of years from now, someone will likely
be staring at a screen and shaking their fist at you because something doesn't quite fit. The more complicated the system, the
higher the likelihood it will break down. But well-planned systems
can last: vehicle VIN numbers lasted 30 years before requiring minor revision in 2008. Once again, this is another balancing act. But
before you get too caught up on planning for infinite longevity,
keep in mind all of it may come crashing down come a merger or
acquisition. Also, don't forget about the part numbers you already
have; you just might be stuck with them.
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Readability
Readability is absolutely critical, people need to quickly parse
through a large amount of part numbers every day and shortterm retention is important. Generic numbering tends to be less
readable without some designed structure or variation (i.e. breaking up long series of numbers with letters or dashes at fixed positions). It's the reason you might remember a telephone number
with an area code, but not your license plate, despite a smaller
namespace. Intelligent numbers can have readability issues for
the very same reasons, or if they just get too long.
Uniqueness
Two parts with the same number is trouble. Some argue that
only generic numbers ensure uniqueness - but that's not really true. You can get the same uniqueness guarantee with the
right PDM/PLM system for intelligent numbering. Generic numbers, which tend to be shorter, can actually increase the chance
of overlap with respect to mergers and acquisitions or cause
confusion with similar supplier part numbers. Nothing ensures
uniqueness in this scenario, but the larger the namespace the
lower the chance for a collision. But once again longer part numbers degrade readability.
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Interpretation
Every time a part is handled, sorted, searched, or otherwise used
an interpretation cost is involved. In other words, it's the time
needed to understand whether you are dealing with the right
part. Intelligent part numbers can reduce this interpretation cost,
provided the user understands the identification system. In the
right conditions, parts can be recognized at a glance. Take caution, however. If the cost of maintaining the intelligent system
exceeds the interpretation cost, it's self-defeating. Generic numbers, on the other hand, can increase interpretation costs, since
differences have to be queried in the system. Generic part interpretation can be enhanced with classification systems, but they
also add cost.
Balancing all these diverse factors is difficult, because no solution
is optimal for every company. Here are some final tips to help you
make prudent decisions:
• Understand your PDM/PLM system part number generation
capabilities.
• Understand the limitations of any other systems that interact
with your parts.
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• Go through every activity that requires interpreting part numbers and understand what system access is available, and how
the interfaces work. This will provide a good basis for your interpretation cost.
• Understand how easy/difficult it is for a new employee to interpret a part number.
DISCUSSION
Ken Schnautz:
Our company has been around for about twelve years, and during
the first ten, we had all sorts of part numbers passing through engineering, inventory, and sales. We had part numbers, assembly
numbers, drawing numbers... all based on job numbers, or product
names, supplier item names or numbers. It was a mess.
About two years ago, (when I started) we finally got deeply involved
in engineering design and recognized the need to make a company-wide item numbering scheme. After a few intense debates and
many meetings later, we settled on a generic sequential numbering plan. Each item is assigned an eight digit number- starting at
10000001 and counting up.
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All items share the same pool of item numbers. This is where it gets
both ugly and beautiful. Parts are items. Assemblies are items. Drawings are items. Documents, forms, templates, finished goods, even
electronic firmware, physical media, and printed drawings. They ALL
are created equal using sequential item numbers.
There is absolutely no room for inference when reading a part number. If I gave you a number, e.g., 10001221 - you don’t know what it
is. It could be a drawing, or a part. You have to look it up! The best
tool to date has been Arena PLM (sorry... I don’t plan on making this
an Arena commercial). It’s a cloud-based service that we use to assign our part numbers, track BOMs, ECOs, revisions, file references...
you get the gist.
Approximately 2500 item numbers later (1.5 years), we’re glad we
made the switch. I have to admit, I’ve spent days explaining the
scheme during the first few months to various groups (engineering, purchasing, sales...) but it’s been a great fit so far. Having the
new PLM has forced us to take better control of our documentation.
Nothing leaves engineering unless it’s released in the PLM system.
Granted, the PLM system has a few kinks (inability to add old-revision
parts to new BOMs), but that is a separate issue that we will have to
resolve by creating new items in lieu of revisions.
All in all, the move to generic item numbering and the fact that ALL
items (drawings, parts, assemblies, media, etc.) share a pool of item
numbers has been the best thing to happen to our company’s docu-
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ment control. The only complaint I’ve heard lately is that we should
have chosen seven digits instead of eight. :)
---- and for those that are curious, we are a industrial product development group. So we do product designs that include custom welded metal, machined metal, injection-molded plastic, machined plastic, cable assemblies/harnesses, printed circuit board assemblies (we
have part numbers for each pcb, resistor, capacitor, IC, ...), software,
firmware, ... the works.---
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HELLO
my name
is
The One True Part
Number System
Ed Lopategui
T
he debate around part number systems is often reduced to
a pitched battle of absolutes, pitting the cold simplicity of the
Generic Numbering Coalition (GNC), against the historically fo-
cused Confederacy of Intelligent Numbers (CIN). There’s no shortage of arguments about one approach over the other. But you
don’t have to play that game; there are always other possibilities.
Let’s understand why.
The GNC was founded on the philosophy that part numbers are
inconsequential. Part numbers are merely unique markers that
point to a collection of metadata, and people shouldn’t bother
with them. Let the machines do the work, keep humans and their
fat-fingering ways out of the loop. After all, even the most elaborately designed intelligent part-numbering system is a temporary
triumph, which will succumb to degradation, confusion, and irrelevancy over time.
CIN, on the other hand, upholds a humanistic appreciation of history. Part numbers are important; they will always be the subject
of conversation, collaboration, and argument between humans
and not systems. And to facilitate those interactions, part numGRABCAD.COM
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bers must provide some system-independent context in of themselves because there comes a time we have to look up from our
screens and communicate one on one. The only way to build such
a context is to architect a recognizable system, and one that lasts.
Which System is Best?
Neither. Both approaches are myopic because they are extremes
that wholly ignore the other’s chief advantage. A balance is needed. A hybrid methodology. But it’s much more than just crafting a
semi-intelligent system and calling it a day. In order to understand
precisely why, consider the following engineering realities:
• Defining a part number should never be an obstacle. An idea
should not be derailed merely because a person has to sit
around and think about what a number should be or how to
get it properly assigned.
• Flexibility is Key. This is especially important for new design.
Sometimes you don't know what you're building until you build
it. Don't force decisions that don't have immediate answers. If
your part numbering system has rigid classification you may
find yourself stuck. The most resilient rules are not absolutes,
but can bend when the situation requires.
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• You should be able to remember several part numbers. If you
can't, then congratulations -you've built a system to welcome
our new robot overlords, but not for people to use.
• Realize the system is not ubiquitous. Relying on the system
for certain information is necessary, but understand there will
always be gaps in the system. We tend to oversell the utility of
mobile tablets, phones, etc. in this regard. The reality is we’re
going to talk about parts in dark corners devoid of technology.
In the hall, on a phone, under a plane, in an adhoc meeting sidebar, or in the vice president’s office. In none of these situations
does everyone in the room have the luxury to sift through a device and sort some classification, just to tell two numbers apart.
It's best to think of it almost from a military standpoint - what do
you need when you're pinned and comms are down?
• Out of the Box (OOTB) tool behavior or current systems should
not limit your solution. You need to fight the limitations to balance your objectives. But only if it makes sense.
But how do we incorporate all of this into something viable?
Here's a thought: how about creating an evolutionary system:
• Use a temporary pool of simple numbers to remove obstacles
when working fast and loose, especially in early-stage design.
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• Allow for easy re-identification (you'll have to fight the tool
here).
• Design gaps in numbering to permit grouping some numbers
together when it makes sense to do so.
• Let the numbers evolve as the design matures, and solidify
those numbers into something that is meaningful through a
release process.
• Construct them with just enough information and structure for
readability, keeping digits in groups of 5 or less.
• Weigh each piece of intelligence carefully, and focus on properties that are both a) useful and b) immutable.
• Consider three bits of information a maximum and not a goal.
If you can balance the above guidelines just right, you might have
a winner on your hands.
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DISCUSSION
JeffMirisola
No. Just no.
All you’ve done here is add in layers of management to, ultimately,
get to an intelligent numbering system which, in the end, is destined
to fail on some front.
Let’s step back and look at it from a different angle: I just got a job
at XYZ Corp working on a project and I know that I need a 1/2” thick
UHMW wear pad. The most logical thing for me to do is go into whatever MRP/ERP system the company has and look up ‘wear pad’. I
certainly wouldn’t pull out whatever cipher was given to me so that I
could go through all the codes to find out if such a part already existed. So, given that logic, I don’t care about the part’s number, I care
about its description and the two shouldn’t be the same - i.e. the part
number shouldn’t be some cryptic description, that’s what the description is for. Granted, this requires some sort of intelligence in the
company’s naming convention (Noun, adjective, further descriptor),
but that’s a lot easier to deal with than some alpha-numeric code
that requires a code breaking class at Quantico.
I realize that some people have differing opinions and, like me, they
aren’t going to be talked into going to the other side, and that’s fine. I
just know that I will forever find intelligent part numbers to be dumb.
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Klaus Brettschneider
Great piece Ed, especially the point that a balance is needed.
As a system integrator, I am a GNC advocate. But I accept history
and established work processes and it is more important to pick the
fights where processes can be improved and where they can be won.
Usually it helps to distinguish what is needed to classify/characterize
a part and what is needed to identify it. A discussion around the difference and the concepts behind will lead to a balance.
One of my golden rules: “Never question smart numbers when the
number system inventor is in the room.”
PS: I’m constantly afraid to meet a smart number system one day
what is smarter than I. ;-)
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GrabCAD.com
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